When Antony Hegarty of Antony and the Johnsons won the Mercury music prize in 2005, he said the prize was like "a contest between an orange and a space ship and a potted plant and a spoon". Even though the Man Booker prize isn't like those late-lamented awards, the Whitbread and the WH Smith, in that it doesn't cross genres, it can still feel like an impossible process of comparing like with unlike. The very richness, diversity and range of the novel in English - or Englishes - which makes judging the prize such an interesting privilege is also what makes it so difficult to do, and so open to debate.

The literary agent Peter Straus sent me a bundle of clippings the other day about the history of the Booker, of which my favourite was an interview with Anita Brookner in 1993, who said, lugubriously: "Winning the Booker has had nil impact on my writing career, and your reputation sinks rapidly after winning." The clippings also included Philip Larkin's 1977 chairman's speech, in which he described himself and his fellow judges as resembling "a bunch of terriers looking for a rat: we couldn't describe it, but we should know it when we found it"; rather a good way of putting it.

We tried to read our way to choosing this year's winner, Kiran Desai's The Inheritance of Loss, without giving way to pressure - and the pressure is considerable. The first lists were organised by publishers, and I asked for them to be re-done so that we would be less aware - and, if possible, try to forget - who the publishers were. We tried to read each novel for itself, not in the light of earlier work or of the author's fame or status or previous prizes. Naively, I suppose, I was rather startled by the amount of extra-literary white noise there was, getting in between us and our books. First there's the apparatus on the proof-copies, which I know is now a necessary part of the publishing process. But I did begin to develop an allergy to phrases like "unputdownable" or "must-read of the year" or "fast-page-turner"; for the adverb "deeply" (as in compassionate, sympathetic, moving - but never as in "putdownable"); and for the "X meets Y" formula, as in "Ian McEwan meets John le Carré", or (my favourite) "Roddy Doyle meets Angela Carter".

I began to ask myself why the promise of "£100,000 marketing campaign including Central London bus sides" or "samplers to be handed out on the streets" or "plasma screens at key commuter stations" should convince me that this was a novel worth reading. I treated with suspicion the novel which came with a red strap-line on the cover reading "Man Booker 2006 Submitted!", or which told me "The Ultimate Experience Is About to Begin", or that it had taken 30 years to write, or which announced itself as "unforgivably nasty" or "appallingly intelligent".

I began to fantasise about manuscripts arriving in brown paper wrappers, with no name, no author photograph, no praise, and no biography. Well, why not? An anonymous Man Booker prize!

Another form of pressure I'd not really thought about before, since I've usually been on the other side of the fence, comes from reviewers who want to tell the judges their business. "Booker judges, take note!", coming from a reviewer whose views you particularly dislike, makes it hard to do justice to that particular novel. "This author's superiority to the average puts him well beyond the competence of Booker judges" struck me as an encomium that could backfire.

Pressure came from the bookmakers' and the booksellers' expectations. The decision seemed generally to have been made for us, once our long-list was announced, that our six short-listed authors were going to be the ones everyone already knew well. I would like to quash the rumour that we deliberately set out to choose less-well-known or younger writers or to do a disservice to some great names in fiction. This was not the case, and it would have been quite wrong of us to do that.

We were very happy to celebrate the great powers and talents of some of the well-known names on out longlist, like David Mitchell, Claire Messud, James Robertson, Peter Carey, Nadine Gordimer and Barry Unsworth - and for me, above all, Andrew O'Hagan and Howard Jacobson. But I have mixed feelings about the existence of the longlist. Although it allows attention and sales for titles which aren't going to make it onto the shortlist, it also adds a double dose of humiliation for the excluded writers, it truncates the judges' initial reading-time by a month, and it emphasises the commercial aspect of the whole process. I myself wish the prize could revert to just having a shortlist, but perhaps a slightly bigger one.

We chose the six books we were most passionate about and which most excited and interested all five of us. And it didn't seem to me that the Man Booker judges should be bearing in mind, in the process of making their decision, what the betting is or might be, what the big bookshop chains want, or even what the general reading public expects. In the fortnight or so after the shortlist was announced, I had difficulty finding the books in the big bookstores, and so did other people I know in different parts of the country. The front tables were piled high with copies of the season's big names - some of them on our long-list - but not with the short-listed books. As I searched for my shortlist in various Waterstone's I began to feel like an organic farmer in a supermarket.

Part of the problem, clearly was "poor availability" from publishers who had been taken by surprise, and did not reprint in time. But I did begin to feel that our list was being overridden or side-lined by commercial imperatives. These aren't the kind of things the judges should be thinking about: we should be able to be independent-minded and unwordly, a strange, protected species of abnormally compulsive readers.

And now we can go back to our ordinary working lives, the 19 novels we liked best can go on - we hope - reaching the audiences they deserve, and what really matters can stand clear of all the fuss: the future of reading, the power of story-telling, the adventure of language.